This invention relates to the field of electronic displays, and, more particularly, flat panel displays, and even more particularly, field emission display (xe2x80x9cFEDxe2x80x9d) devices.
As technology for producing small, portable electronic devices progresses, so does the need for electronic displays which are small, provide good resolution, and consume small amounts of power in order to provide extended battery operation. Past displays have been constructed based upon cathode ray tube (xe2x80x9cCRTxe2x80x9d) or liquid crystal display (xe2x80x9cLCDxe2x80x9d) technology. However, neither of these technologies is perfectly suited to the demands of current electronic devices.
CRT""s have excellent display characteristics, such as, color, brightness, contrast and resolution. However, they are also large, bulky and consume power at rates which are incompatible with extended battery operation of current portable computers.
LCD displays consume relatively little power and are thin in size. However, by comparison with CRT technology, they provide poor contrast, and only limited ranges of viewing angles are possible. Further, color versions of LCDs also tend to consume power at a rate which is incompatible with extended battery operation.
As a result of the above described deficiencies of CRT and LCD technology, efforts are underway to develop new types of electronic displays for the latest electronic devices. One technology currently being developed is known as xe2x80x9cfield emission display technology.xe2x80x9d The basic construction of a field emission display, or (xe2x80x9cFEDxe2x80x9d) is shown in FIG. 1. As seen in the figure, a field emission display, also referred to as a xe2x80x9cflat panel display,xe2x80x9d comprises a faceplate 100 with a transparent conductor 102 formed thereon. Phosphor dots 112 are then formed on the transparent conductor 102. The faceplate 100 of the FED is separated from a baseplate 114 by a spacer 104. The plates 100 and 104 are also referred to as substrates. The spacers serve to prevent the baseplate from being pushed into contact with the faceplate by atmospheric pressure when the space between the baseplate and the faceplate is evacuated. A plurality of emitters 106 are formed on the baseplate. The emitters 106 are constructed by thin film processes common to the semi-conductor industry. Numerous emitters 106 are formed on the baseplate 114 to provide a spatially uniform source of electrons.
During manufacturing, a seal is formed around the outer boundaries of the faceplate 100 and the baseplate 114 to contain the evacuated space between them. Before this seal can be formed, it is important that the faceplate 100 is accurately aligned with the baseplate 114 in order to produce an acceptable flat panel display. In order to obtain the necessary alignment, corresponding alignment marks are often placed on the faceplate 100 and the baseplate 114. Optical equipment for detecting these alignment marks is then used to ensure that the plates are properly aligned. FIG. 1B shows an example of such alignment marks. As shown, substrate 100 is patterned with alignment marks 102. Substrate 100 may be either a faceplate or a baseplate. Substrate 104 is provided with alignment marks 106 which correspond to alignment marks 102 on substrate 100. As the substrates are assembled, optical equipment is used to simultaneously observe alignment marks 106 and 102 to ensure proper alignment of the substrates.
However, this technique is not completely satisfactory. In order for the optical equipment to ensure that the substrates are properly aligned, the equipment must be able to accurately focus on the edges of alignment marks 102 and 106. Further, the optical equipment must be able to focus on alignment marks 102 and 106 simultaneously as the substrates are being aligned. Such accurate focusing of the optical equipment is difficult due to the relatively large spacing between the substrates in a flat panel display. Moreover, the problem is compounded because, as the magnifying power of the optics is increased to provide an accurate image of the alignment marks, the depth of focus is correspondingly decreased thus making it even more difficult to focus on both substrates simultaneously. For example, for a flat panel display having a 500 micron gap between substrates 100 and 106, there are no optics presently available which would provide a micron (order of magnitude) accuracy. Further still, optics capable of producing an acceptable alignment are expensive and add to the overall cost of the manufacture of the flat panel display.
Accordingly, there is a need in the art for a method and apparatus of aligning flat panel displays which will overcome the above-mentioned problems.
According to an aspect of the present invention, there is provided a method of aligning substrates in an apparatus for aligning a flat panel display having a plurality of substrates. Although the following discussion often focuses on field emissions displays, it is to be understood that the present invention also has application with other flat panel displays such as LCDs and plasma displays. In one embodiment, the method for aligning the substrates comprises providing an optical path through each substrate, wherein alignment of the optical paths corresponds a desired alignment of the substrates. In another aspect, the invention comprises directing a light into the optical path of a first substrate, detecting the light exiting the optical path of a second substrate and positioning the substrates relative to each other such that the amount of detected light is optimized.
According to another embodiment of the invention, there is provided an apparatus for aligning a plurality of substrates in a field emission display, each substrate having a path allowing for the passage of light, the paths being disposed such that alignment of the paths corresponds to a desired alignment of the substrates. In one version, the apparatus has a source which directs a light into the optical path of a first substrate, a detector of the light exiting the optical path of a second substrate, and a positioner which determines the amount of light detected and positions the substrates relative to each other such that the amount of detected light is optimized.